Annealing apparatus using two wavelengths of radiation

Abstract

A thermal processing apparatus and method in which a first laser source, for example, a CO 2 emitting at 10.6 μm is focused onto a silicon wafer as a line beam and a second laser source, for example, a GaAs laser bar emitting at 808 nm is focused onto the wafer as a larger beam surrounding the line beam. The two beams are scanned in synchronism in the direction of the narrow dimension of the line beam to create a narrow heating pulse from the line beam when activated by the larger beam. The energy of GaAs radiation is greater than the silicon bandgap energy and creates free carriers. The energy of the CO 2 radiation is less than the silicon bandgap energy so silicon is otherwise transparent to it, but the long wavelength radiation is absorbed by the free carriers.

The invention claimed is: 
     
       1. A thermal processing system, comprising:
 a stage; 
 a first source of a first continuous-wave radiation having a wavelength of at least about 1.2 μm; 
 a first optical assembly to shape the first radiation into a first beam onto a first area of the stage having a first dimension extending along a first axis and a second dimension longer than the first dimension extending along a second axis transverse to the first axis; 
 a second source of a second continuous-wave radiation of visible light having a wavelength less than about 1 μm; and 
 a second optical assembly to shape the second radiation into a second beam onto a second area of the stage that surrounds the first area. 
 
     
     
       2. The thermal processing system of  claim 1  further comprising:
 a translation mechanism to scan the first and second beams relative to the stage while the second beam surrounds the first beam. 
 
     
     
       3. The thermal processing system of  claim 1 , wherein the first source comprises a CO 2  laser. 
     
     
       4. The thermal processing system of  claim 3 , wherein the second source comprises a diode laser source. 
     
     
       5. The thermal processing system of  claim 1 , wherein first and second sources and the first and second optical assemblies are configured to direct the first beam and the second beam onto the stage concurrently. 
     
     
       6. The thermal processing system of  claim 1 , wherein a center of the first area substantially coincides with a center of the second area. 
     
     
       7. A thermal treatment apparatus for heating a semiconductor substrate, comprising:
 a stage; 
 a source of activating energy of continuous-wave visible light to create free carriers within a layer of the semiconductor substrate; 
 a source of heating energy of continuous-wave infrared radiation to heat the semiconductor substrate; 
 a first optical assembly to shape the activating energy into a first beam and direct the first beam onto a first area of the stage; and 
 a second optical assembly to shape the heating energy into a second beam and direct the second beam onto a second area of the stage, wherein the first area surrounds the second area. 
 
     
     
       8. The thermal treatment apparatus of  claim 7 , wherein the sources of activating and heating energy and the first and second optical assemblies are configured to direct the first beam and the second beam onto the stage concurrently. 
     
     
       9. The thermal treatment apparatus of  claim 7 , further comprising a translation mechanism to translate the stage or the first and second beams while maintaining the first area surrounding the second area. 
     
     
       10. An apparatus for thermally treating a semiconductor substrate having a bandgap energy, comprising:
 a short-wavelength source of continuous-wave visible electromagnetic radiation having a photon energy greater than the bandgap energy of the semiconductor substrate; 
 a long-wavelength source of continuous-wave electromagnetic radiation having a photon energy less than the bandgap energy of the semiconductor substrate; 
 a stage; and 
 optics interposed between the stage and the short-wavelength and long-wavelength sources to direct the short-wavelength source as a short-wavelength incident beam on a first area of the stage and to direct the long-wavelength source as a long-wavelength incident beam on a second area of the stage, wherein the first area surrounds the second area. 
 
     
     
       11. The apparatus of  claim 10 , wherein a center of the first area substantially coincides with a center of the second area. 
     
     
       12. The apparatus of  claim 10 , wherein the short-wavelength source, long-wavelength source and the optics are configured to direct the short-wavelength incident beam and the long-wavelength incident beam onto the stage concurrently. 
     
     
       13. The apparatus of  claim 10 , wherein the semiconductor substrate comprises silicon.